Aircraft cockpit display panel illumination systems are designed around the output of a filament based incandescent light source (incandescent filament lamps), which is measured in mean spherical candle power (MSCP) radiating light in a spherical emission pattern. The incandescent lamps operate from standard 14 VDC or 28 VDC aircraft electrical power systems. Current aircraft cockpit panel illumination systems were designed for incandescent filament lamps, which require little or no thermal transfer.
An LED lamp is a type of solid state lighting that uses light-emitting diodes (LEDs) as the source of light, rather than electrical filaments. A typical LED, however, produces non-uniform radiation patterns primarily due to packaging constraints. Accordingly, typical LED lamps produce unsatisfactory illumination appearance. A typical miniature LED lamp incorporates only a single LED, which has a forward voltage drop of anywhere from about 2 VDC to about 3.5 VDC.
Replacing incandescent filament lamps with LED lamps in aircraft cockpit display panel illumination systems has proven challenging because of the power dissipation associated with typical LED lamps. A basic LED lamp used in an aircraft cockpit display panel illumination system requires a dropping resistor in series with the LED to offset the 14 VDC or 28 VDC aircraft electrical power operating system. The product of excess voltage dropped across the resistor and current through the resistor manifests itself as heat, which must be dissipated. Generally, the dropping resistor is formed integrally with the LED lamp assembly. For this reason, excess heat produced by the dropping resistor can eventually lead to premature failure of the LED lamp assembly. In order to increase the life and reliability of the LED lamp, the heat must be drawn away from the LED. However, as previously discussed, current aircraft cockpit panel illumination systems designed for incandescent filament lamps, which require little or no thermal transfer, do not provide adequate ventilation or cooling for drawing excess heat from the LED lamp assembly. Therefore, the heat generated in a typical LED lamp cannot escape, resulting in lower light output, decreased life expectancy, and premature failure due to higher operating temperatures.
Accordingly, there is a need for an improved efficient solid state lamp based illumination device for illuminating aircraft cockpit displays, instrument panels, avionics, switch panels, and aircraft interiors.